Resist pattern forming method

ABSTRACT

A resist pattern forming method includes preparing a photomask for generating near-field light having an intensity distribution. The photomask has a light-transmissible base member, and a light-blocking film. The film has a micro-aperture adapted to expose an object to near-field light seeping out from the micro-aperture. The photomask has a periodic structure and a shift of a phase. The shift exists between recesses or projections adjacent to the micro-aperture. A difference in the intensity distribution of the near-field light in the area of the aperture is reduced. The photomask is arranged close to a photoresist film on a substrate. Light from a light source irradiates the photoresist film by way of the photomask to form a latent image based on the micro-aperture, and the photoresist film is developed to form a resist pattern on the substrate based on the latent image.

This application is a divisional application of copending U.S. patentapplication Ser. No. 10/842,451, filed May 11, 2004.

This application also claims priority from Japanese Patent applicationNo. 2003-132517 filed on May 12, 2003, the entire contents of which ishereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photomask for exposure to an opticalnear-field, to a method of controlling an optical near-field intensitydistribution using such a photomask, to a pattern preparing method, andalso to a pattern preparing apparatus.

2. Related Background Art

With the current advancement of technology brought forth to realizesemiconductor memories having a higher memory capacity and CPUs thatoperate at a very high speed, and show an enhanced degree ofintegration, photolithography is inevitably required to accommodatemicro-processing operations with smaller dimensions. Generally, thedimensional limit of micro-processing of a photolithography apparatusapproximately corresponds to the wavelength of the light source to beused for photolithography. Therefore, a near-ultraviolet laser is oftenused as a light source for a photolithography apparatus in order toreduce the dimensional limit. Thus, currently, photolithographyapparatuses are feasible for micro-processing on the order of about 0.1μm.

While the dimensional limit of micro-processing is reduced forphotolithography, there are still a number of problems to be solved forphotolithography if it is to be used for micro-processing of 0.1 μm andless. For example, a light source having a shorter wavelength may beneeded. Then, lenses that can be used for such a short wavelength mayhave to be developed.

Near-field exposure methods have been proposed as a possible solutionfor these problems. For example, U.S. Pat. No. 6,171,730 proposes anexposure method and an exposure apparatus that utilize an elasticallydeformable mask having a micro-aperture pattern of an opening with awidth not greater than 100 nm on the front surface and made of anelastic material so as to be deformable along the normal line relativeto the mask surface. The method and the apparatus as disclosed in theabove-cited patent document are excellent, and have contributed greatlyto the technological field to which the present invention relates.

However, when g-rays having a wavelength of 436 nm or i-rays having awavelength of 365 nm are used for a micro-aperture pattern with a widthnot greater than 100 nm, as disclosed in U.S. Pat. No. 6,171,730, thewidth of the openings is less than one half of the wavelength.

In an operation of near-field exposure using a near-field formed bylight by way of a micro-aperture in a metal film, the optical near-fieldintensity distribution can be different from the contour of theaperture.

Meanwhile, U.S. Pat. No. 6,236,033 proposes a photolithography maskformed on a metal film and having an aperture and a surface profile thatundulates periodically so as to interact with surface plasmon modes andintensifies the transmission of light through the aperture for thepurpose of transferring an image. However, while the above-cited patentproposes to boost light obtained through the aperture, it does notpropose to weaken light and make uniform the intensity distribution oflight.

SUMMARY OF THE INVENTION

The present invention provides a photomask for exposure to an opticalnear-field, a method of controlling an optical near-field intensitydistribution using such a photomask, a pattern preparing method and alsoa pattern preparing apparatus, as will be described hereinafter.

In an aspect of the invention, there is provided a photomask forexposure to an optical near-field having a micro-aperture and adapted toexpose an object of exposure to light by using light seeping out fromthe micro-aperture, the mask having periodically arranged recesses orprojections so as to make uniform the optical near-field intensitydistribution in the micro-aperture.

For the purposes of the invention, the aperture width of themicro-aperture may be not greater than one-half of the wavelength oflight from the light source.

For the purpose of the invention, the optical near-field intensitydistribution may be controlled by way of the positions and/or sizes ofthe recesses or projections relative to the micro-aperture.

The recesses or projections may be arranged periodically relative to themicro-aperture and the optical near-field intensity distribution may becontrolled by way of the extent of shift of the pitch and/or the phaseof the period.

The pitch of the period may be made shorter than the intra-mediumwavelength of the light used for the exposure within the mask basemember of the photomask.

For the purpose of the invention, it may be so arranged that themicro-aperture includes a micro-aperture group of a plurality ofmicro-apertures and the photomask has the recesses or projections in thevicinity of an area of a weak optical near-field intensity that isproduced when light for exposure is applied in the micro-aperture group.

Alternatively, it may be so arranged that the micro-aperture includes amicro-aperture group of a plurality of micro-apertures and the photomaskhas the recesses or projections in the vicinity of an area of a strongoptical near-field intensity that is produced when light for exposure isapplied in the micro-aperture group.

For the purposes of the invention, it may be so arranged that themicro-aperture includes a micro-aperture group of a plurality ofmicro-apertures and the photomask has at least a first recess or aprojection in the vicinity of an area of a weak optical near-fieldintensity that is produced when light for exposure is applied in themicro-aperture group, the first recess or projection and the secondrecess or projection being different from each other in terms ofrelative position and/or size relative to the micro-aperture.

Still, alternatively, it may be so arranged that the micro-apertureincludes a micro-aperture group of a plurality of micro-apertures andthe photomask has first recesses or projections arranged periodically inthe vicinity of an area of a weak optical near-field intensity that isproduced when light for exposure is applied in the micro-aperture groupand second recesses or projections arranged periodically in the vicinityof an area of a strong optical near-field intensity that is producedwhen light for exposure is applied in the micro-aperture group, thefirst recess or projection and the second recess or projection beingdifferent from each other in terms of the pitch and/or phase of period.

For the purposes of the invention, it may be so arranged that themicro-aperture is slit-shaped and the photomask has the area of a weakoptical near-field intensity in the vicinity of each of the ends of theslit-shaped micro-aperture, the recess or projection being formed in thevicinity of each of the ends of the slit-shaped micro-aperture.

For the purposes of the invention, it may be so arranged that themicro-aperture shows an isolated pattern having a longitudinal dimensionand a transversal dimension smaller than the wavelength, and the area ofweak optical near-field intensity is located in the vicinity of theisolated pattern, whereas the recess or projection is formed in thevicinity of the isolated pattern.

For the purposes of the invention, it may be so arranged that the phaseof the period forms a discontinued section in the periodically arrangedrecesses or projections and the discontinued section is arranged in thevicinity of the micro-aperture.

For the purposes of the invention, it may be so arranged that themicro-aperture includes a micro-aperture group of a plurality ofmicro-apertures and the photomask is provided with a first periodicstructure having a discontinued section in the phase of the period inthe vicinity of an area of a weak optical near-field intensity that isproduced when light for exposure is applied in the micro-aperture groupand a second periodic structure having a discontinued section in thephase of a period in the vicinity of an area of a strong opticalnear-field intensity that is produced when light for exposure is appliedin the micro-aperture group, the amount of discontinuation of phasebeing different between the first periodic structure and the secondperiodic structure.

In another aspect of the present invention, there is provided a methodof controlling an optical near-field intensity distribution using aphotomask for exposure to an optical near-field according to theinvention and adapted to control the intensity distribution of theoptical near-field according to the invention and adapted to control theintensity distribution of the optical near-field by adjusting thecoupled relation of light being propagated through the micro-apertureand plasmon polaritons on the surface of the photomask.

In still another aspect of the invention, there is provided a patternpreparing method comprising arranging a photomask for exposure to anoptical near-field on a substrate to be processed, the substratecarrying a photoresist film thereon with a thickness not greater thanthe wavelength of light from a light source, irradiating light forexposure from the light source onto the photoresist film by way of thephotomask, and forming/transferring a latent image on the photoresistfilm on the basis of the aperture pattern formed in the photomask bycontrolling the intensity distribution of the optical near-field.

In still another aspect of the invention, there is provided a patternpreparing apparatus comprising a stage adapted to carry thereon aphotomask for exposure to an optical near-field according to theinvention, a light source for exposure, a specimen table adapted tocarry thereon a substrate to be processed, the substrate carrying aphotoresist film thereon with a thickness not greater than thewavelength of light from the light source, and a distance control meansfor controlling the distance between the substrate to be processed andthe photomask.

Thus, according to the invention, it is possible not only to control theintensity distribution of the optical near-field, at will, but it isalso possible to provide a photomask for exposure to an opticalnear-field that can control the intensity distribution so as to make ituniform, a method of controlling the intensity distribution of anoptical near-field by using such a photomask, a pattern preparing methodand a pattern preparing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the first embodiment of aphotomask for exposure to an optical near-field according to theinvention;

FIG. 2 is a schematic illustration of a photomask for exposure to anoptical near-field obtained by modifying the first embodiment of theinvention;

FIG. 3 is a schematic illustration of the second embodiment of aphotomask for exposure to an optical near-field according to theinvention;

FIG. 4 is a schematic illustration of the third embodiment of aphotomask for exposure to an optical near-field according to theinvention;

FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G and 5H are numerical computation modelsof an optical near-field in a near-field micro-aperture produced byperiodically arranged recesses and projections provided for the purposeof explaining the first embodiment of the invention;

FIG. 6 is a graph obtained by computationally determining the intensitydistribution of an optical near-field provided for the purpose ofexplaining the first embodiment of the invention;

FIG. 7 is a contour graph illustrating the pitch lambda (nm) of theperiodic structure and the intensity of light immediately below theaperture, relative to the phase, as provided for the purpose ofexplaining the first embodiment of the invention;

FIG. 8 is a schematic illustration of the pattern preparing apparatusused in Example 1; and

FIGS. 9A, 9B, 9C and 9D are schematic illustrations of the patternpreparing method used in Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described in greater detail byreferring to the accompanying drawings.

First Embodiment

FIG. 1 is an enlarged partial view of the first embodiment of aphotomask for exposure to an optical near-field according to theinvention. The photomask comprises a base member 101 that is transparentrelative to the wavelength of light from a light source to be used forexposure and a metal thin film 102 that blocks light from the lightsource. The thin film has a thickness between 40 and 200 nm.

The base member 101 is also a thin film having a thickness between 0.1and 100 μm that is supported along the outer peripheral section thereofby a support member (not shown). The metal thin film 102 has aslit-shaped aperture 103. The width of the slit is smaller than half ofthe wavelength of light from the light source, whereas the length of theslit is greater than the wavelength of light from the light source.

Recesses/projections 104 are formed periodically in the vicinity of eachof the ends of the slit of the metal film 102 in a directionperpendicular to the longitudinal direction of the slit (in thedirection of AA′ in FIG. 1).

The mask is made to tightly adhere to the thin film resist applied to asubstrate. Then, light is irradiated onto it in a directionperpendicular to it so that the pattern is exposed to light. Now, thebehavior of light in the vicinity of the mask will be discussed indetail below.

When light for exposure is irradiated onto the mask from the side of thebase member, an optical near-field is produced in the vicinity of theaperture on the front surface of the mask (the surface at the lower sidein the cross-sectional view of FIG. 1).

The periodic recesses/projections 104 at each of the ends of the slit ofthis embodiment are designed to boost the intensity of light at a partof the slit located near the recesses/projections, so as to minimize thedifference in the optical near-field intensity over the entire area ofthe mask aperture and to realize a quasi-flat light intensitydistribution pattern.

The distributed optical near-field is weak in the vicinity of each ofthe ends of the slit when there are no periodic recesses/projections104, for the reason described below.

Assume that light is irradiated onto the mask of FIG. 1 withoutcontrolling polarization of the light. The incident light can be dividedinto a parallel component whose electrical field vector is parallel tothe slit and a perpendicular component whose electrical field vector isperpendicular to the slit. The slit does not allow the component oflight whose electrical field vector is parallel to the slit (and, hence,parallel to the metal surfaces, or the lateral surfaces, of the slit) topass through it. On the other hand, the component of light whoseelectrical field vector is perpendicular to the slit is propagatedthrough the slit and produces an optical near-field on the front surfaceof the mask. However, the propagation loss of light is increased in theslit, because the electrical field vector runs parallel with the metalsurface at each of the ends of the slit. Such a loss affects the rangefrom the ends of the slit to the wavelength of light from the lightsource.

The concept of controlling the intensity of light by means of periodicrecesses/projections 104 arranged near the slit is based on theprinciple as described below. The periodic recesses/projections 104control coupling of interface plasmon polaritons and light that is beingpropagated through the slit on the surface of the metal film (theinterface of the metal film and the base member or the interface of thephotoresist and the metal film when the metal film tightly adheres tothe photoresist).

More specifically, interface plasmon polaritons are scattered by theperiodic recesses/projections to give rise to a standing wave. Theintensity of an optical near-field is boosted if the position of theslit is found near a loop of the standing wave, whereas it is weakenedif the position of the slit is found near a node of the standing wave.

This effect will be described further by way of specific numeralcomputation models, as shown in FIGS. 5A through 5H. Chromium (Cr,complex refractive index; 1.775-4.035i) is used as a metal, and a valueof 436 nm is assumed for the wavelength in a vacuum of light from alight source. For the purpose of simplicity, two-dimensional modelswhere the refractive index of the base member is equal to one, and theslit has an infinite length, are used.

First, two parameters of the pitch Λ and the phase Φ ofrecesses/projections that are used for describing the profile ofperiodic recesses/projections in a case wherein there is no slit will beexplained by referring to FIGS. 5A through 5D. A slit is to be arrangedalong the dotted chain line in each of FIGS. 5A through 5D. However, thephase and the pitch are defined on the basis of the profile of therecesses/projections before arranging a slit. The pitch Λ is thedistance for a period of a recess and a projection, as shown in FIG. 5A.Phase Φ=0 is defined for the periodic structure of FIG. 5A where thephase does not show any discontinuity at the axis of symmetry and thelatter is the center of a recess. On the other hand, phase Φ=π/4 isdefined for the periodic structure of FIG. 5B, phase Φ=π/2 defined forthat of FIG. 5C, and phase Φ=π is defined for that of FIG. 5D.

While the phase Φ is equal to π also at the left side of the slit, andthere is no discontinuity of phase in the periodic recesses/projectionsof FIG. 5D, the periodic structure of FIG. 5D differs from that of FIG.5A in terms of phase.

FIGS. 5E through 5H show periodic structures where a slit is arranged atthe axis of symmetry and correspond, respectively, to FIGS. 5A through5D. Note, however, that the recess where the slit is arranged is buriedin each of FIGS. 5E and 5F. Two recesses are arranged at each side ofthe slit.

Then, light is irradiated onto the structure form the side where therecesses are formed periodically, and the intensity distribution of anoptical near-field is determined by numerical analysis, using the FDTDmethod. The slit has a width of 80 nm and the light shielding film has athickness of 60 nm.

FIG. 6 shows the computationally obtained values of the intensity oflight (a squared amplitude of the electrical field) at positionsseparated from the mask surface by 10 nm. In FIG. 6, the solid lineindicates the intensity distribution of an optical near-field when noperiodic recesses are arranged. It is provided as a reference forcomparison. On the other hand, the intensity of light is increased byabout 1.5 times relative to the reference value when recesses arearranged periodically with a pitch of Λ=410 nm and a phase of Φ=π/2(dotted chain line), whereas it is reduced to about 0.6 times relativeto the reference value when recesses are arranged periodically with apitch of Λ=340 nm and a phase of Φ=0 (broken line). The pitch that isused to increase the intensity of light is close to the wavelength ofsurface plasmons along the vacuum/Cr interface, or

λspp=λ ₀[(∈_(m)+∈_(d))/(∈_(m)×∈_(d))]^(1/2)=428.4 nm,

but does not completely agree with the latter. In the above formula,∈_(m) represents the dielectric constant of Cr and ∈_(d) represents thedielectric constant of the dielectric substance involved (e.g., a vacuumin the computation models).

FIG. 7 is a contour graph illustrating the pitch lambda (nm) of theperiodic structure, as shown in any of FIGS. 5A through 5H, and theintensity of light immediately below the aperture relative to the phase(deg), where the intensity of light is made equal to one when there isno periodic structure. As in the case of the numerical computationmodels of FIGS. 5A through 5H, chromium (Cr, complex refractive index;1.775-4.035i) is used as a metal, and a value of 436 nm is assumed forthe wavelength in a vacuum of light from a light source. Again, for thepurpose of simplicity, two-dimensional models where the refractive indexof the base member is equal to one, and the slit has an infinite length,are used.

For the effect of intensifying an optical near-field by means ofperiodic recesses/projections, as used in the above computation models,to appear only in regions surrounding the respective ends of the slitwhere the intensity of the optical near-field falls, it is necessary toform periodic recesses/projections only in the vicinity of each of theends of the slit of the mask. When the refractive index of the basematerial of the photoresist that is tightly adhering to the mask is notone, as used in the above-described numerical computation models but n,it is necessary to multiply the above-cited pitch Λ of the arrangementof periodic recesses/projections by 1/n to obtain Λ/n.

In this way, it is possible to obtain a distribution of an intensitythat approximately reflects the shape of the slit, and hence, to form aresist pattern that approximately reflects the shape of the slit, byappropriately controlling the optical near-fields intensitydistribution, using a photomask on which the pitch and/or the phase ofthe periodically arranged recesses are appropriately selected. Whileperiodic recesses/projections are formed only on the surface of themetal film that is irradiated with light in the above description,periodic recesses/projections may alternatively be formed on the frontsurface of the mask, although the effect will be weakened to a certainextent. Still, alternatively, periodic recesses/projections may beformed on the opposite surfaces of the metal film.

While recesses are formed in the above-described instance, it may beneedless to say that a similar effect is obtained by forming periodicprojections.

FIG. 2 shows a modified arrangement of periodic recesses, where squarerecesses are formed around a single micro-aperture to obtain a maskpattern that can effectively increase the optical near-field intensitydue to the arrangement of the periodic recesses.

Second Embodiment

FIG. 3 is an enlarged partial view of the second embodiment of aphotomask for exposure to an optical near-field, according to theinvention. With this embodiment, the intensity of an optical near-fieldcan be reduced by means of periodic recesses for the purpose ofcontrolling the intensity of the optical near-field.

The mask pattern of FIG. 3 is formed by arranging periodic recesses 304in the vicinity of a middle part of slit-shaped aperture 303, where theintensity of the optical near-field is high. In this case, both theintensity of light propagated through the slit and that of the opticalnear-field on the surface of the mask are reduced by shifting the pitchand the phase of the periodic recesses 304.

With this arrangement again, it is possible to control the opticalnear-field intensity distribution in the vicinity of the slit and toobtain an exposure pattern that approximately reflects the shape of theslit.

In a case of controlling the optical near-field intensity distributionnot only for a single slit, but the respective optical near-fieldintensity distributions for a plurality of slits whose shapes may varyfrom each other, so as to obtain a resist pattern, as the whole maskpattern, having a desired profile, the use of such a pattern that canreduce the intensity of the optical near-field is effective.

Third Embodiment

FIG. 4 is an enlarged partial view of the third embodiment of aphotomask for exposure to an optical near-field according to theinvention. With this embodiment, the intensity of the optical near-fieldcan be reduced in certain regions and, at the same time, increased inother regions on the mask by using a plurality of micro-apertures.

The mask pattern illustrated in FIG. 4 is formed by arranging a group ofslit-shaped apertures 403 that run in parallel with each other. Recesses404 are arranged periodically in the vicinity of each of the ends of thegroup of slit-shaped apertures 403 for the purpose of intensifying anoptical near-field, whereas recesses 405 are arranged periodically inthe vicinity of a central part of the group of slits for the purpose ofreducing the intensity of an optical near-field.

With the periodic arrangement of recesses, it is possible to control notonly the optical near-field intensity distribution in a single slit, butalso, the difference in the intensities of an optical near-field amongthe plurality of slits, so as to expose a resist pattern thatcorresponds to the shapes of the slit to light.

Now, the present invention will be described further by way of examples.

Example 1

FIG. 8 is a schematic illustration of the pattern preparing (exposure)apparatus used in Example 1.

In FIG. 8, reference symbol 801 denotes a photomask according to theinvention as described above by way of embodiments. The front surface(the lower surface shown in FIG. 8) of the photomask 801 is directed tothe outside of pressure adjustable container 805, whereas the rearsurface (the upper surface shown in FIG. 8) of the photomask 801 isdirected to the inside of the pressure adjustable container 805. Theinternal pressure of the pressure adjustable container 805 can beadjusted by a pressure adjusting means 813.

The object of exposure in this example was a substrate 806 carrying aresist film 807 that was formed on the surface thereof. The resist807/substrate 806 was placed on a stage 808 and the stage 808 was drivenso as to align the substrate 806 relative to the photomask 701 inintra-planar two-dimensional directions of the mask. Subsequently, thestage 808 was driven in a direction along the normal line relative tothe mask surface so as to make the photomask 801 tightly adhere to theresist 807 on the substrate 806.

Then, the evanescent light exposure mask 801 was made to tightly adhereto the resist 807 on the substrate 806 by adjusting the internalpressure of the pressure adjustable container 805 by the pressureadjusting means 813 until the gap between the front surface of the mask801 and the corresponding surface of the resist 807 became not greaterthan 100 nm over the entire surface area of the mask 801.

Thereafter, light for exposure 810 emitted from light source 809 wascollimated by a collimator lens 811, and then made to pass through aglass window 812 so as to be introduced into the pressure adjustablecontainer 805 and irradiated onto the evanescent light exposure mask 801from the rear surface thereof (upper surface in FIG. 8). The resist 807was exposed to an optical near-field produced in the vicinity of themicro-apertures on the front surface of the photomask 801. It waspossible to transfer the different patterns 804 on the photomask on thesubstrate 806 as patterns of clear contrast by using the photomask 801.

Example 2

FIGS. 9A through 9D are schematic illustrations of the pattern preparingmethod including a single buffer layer used in Example 2.

FIG. 9A shows the photomask and the object of exposure of this example.The photomask 904 is a photomask according to the invention as describedabove by way of the embodiments.

In this example, a positive type photoresist was applied onto an Sisubstrate 901 by means of a spin coater. Subsequently, the photoresistwas heated at 120° C. for thirty minutes to produce the first layer 902,which had a film thickness of 700 nm.

Thereafter, a negative type photoresist that contained Si was appliedonto the first layer 902 and pre-baked to produce the second layer 903,which had a film thickness of 40 nm. Thus, the photoresist had atwo-layered structure.

Then, the Si substrate 901 carrying the two-layered photoresist thereon,which was formed as a result of the application process, was broughtclose to the photomask 904 by means of the exposure apparatus as shownin FIG. 8, and pressure was applied thereto in order to make the resistlayer 903 tightly adhere to the photomask 904.

Light for exposure 905 (the photomask was prepared to meet thewavelength of light) was irradiated onto the photoresist layer 903 onthe substrate 901 by way of the photomask. In other words, thephotoresist layer 903 was exposed to light by way of the patterns on thephotomask 904 (FIG. 9B).

Subsequently, the photomask was removed from the surface of thephotoresist layer 903, which was then subjected to a development processand a post-baking process. As a result, the patterns on the photomaskwere transferred as resist patterns (FIG. 9C).

Thereafter, the first photoresist layer 902 was subjected to an oxygenreactive ion etching process, using the patterns formed on the secondphotoresist layer 903 as an etching mask (FIG. 9D).

The Si contained in the second photoresist layer 903 was oxidized in theoxygen reactive ion etching process to raise the etching-resistance ofthe layer.

As a result of following the above-described procedure, it was possibleto transfer the different patterns on the photomask on the substrate 901as patterns of clear contrast.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

1-18. (canceled)
 19. A resist pattern forming method comprising: (a)preparing a photomask for generating near-field light, the photomaskcomprising: (i) a light-transmissible base member; and (ii) alight-blocking film provided on the base member, the film having amicro-aperture adapted to expose an object to near-field light seepingout from the micro-aperture, the photomask having a periodic structurecomprising the micro-aperture at an axis of symmetry and recesses orprojections with a pitch, and a shift of a phase, wherein the shift ofthe phase exists between the recesses or projections adjacent to themicro-aperture, and wherein an intensity distribution of the near fieldlight is controlled by way of the pitch and an extent of the shift ofthe phase of the periodic structure so that a difference in theintensity distribution of the near-field light in the area of theaperture is reduced; (b) arranging the photomask close to a photoresistfilm on a substrate; (c) irradiating light from a light source onto thephotoresist film by way of the photomask to form a latent image based onthe micro-aperture of the photomask; and (d) developing the photoresistfilm to form a resist pattern on the substrate based on the latentimage.
 20. A resist pattern forming method according to claim 19,wherein a buffer resist layer is interposed between the photoresist filmand the substrate.
 21. A resist pattern forming method according toclaim 20, wherein the photoresist film contains silicon.
 22. A resistpattern forming method according to claim 20, wherein the buffer resistlayer is subjected to an etching process using the resist pattern of thephotoresist film as an etching mask.